Waste heat utilization device and control method thereof

ABSTRACT

A waste heat utilization device includes a Rankine cycle in which an operation fluid circulates, and a control unit which controls an operation of the Rankine cycle. The Rankine cycle has a heater for heating the operation fluid using a waste fluid with a waste heat from a heat engine, an expander that expands the heated operation fluid to recover a mechanical energy, and a condenser for cooling and condensing the expanded operation fluid. The control unit operates the Rankine cycle when a waste fluid temperature is not less than a predetermined temperature and when the waste fluid is in a flowing state in the heat engine.

CROSS REFERENCE TO RELATED APPLICATION

This application is based on Japanese Patent Applications No. 2006-115924 filed on Apr. 19, 2006, and No. 2007-029566 filed on Feb. 8, 2007, the contents of which are incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a waste heat utilization device and a control method thereof. For example, the waste heat utilization device can be used for recovering a waste heat of a vehicular engine.

2. Description of the Related Art

Conventionally, in a vehicle having a Rankine cycle, the Rankine cycle is operated only when a temperature (waste heat) of an engine-cooling water is not less than a predetermined temperature, and the Rankine cycle is stopped when the temperature is not sufficient, for example, as described in U.S. Pat. No. 6,928,820 (corresponding to JP-A-2005-155336). Therefore, an engine temperature can be prevented from decreasing excessively, and the waste heat recovery can be performed without reducing a fuel consumption rate of the engine.

However, when a mechanical pump driven by the engine is used as a pump for circulating the engine-cooling water in a vehicle, such as a hybrid vehicle and an idling stop vehicle, in which the engine may be stopped in accordance with a driving state even when the vehicle is in use, the engine-cooling water is not circulated when the engine is stopped. Therefore, the Rankine cycle may not function as a waste heat recovery system when the Rankine cycle is operated only based on the temperature of the engine-cooling water.

SUMMARY OF THE INVENTION

In view of the foregoing problems, it is an object of the present invention to provide a waste heat utilization device which can ensure a waste heat recovery, and a control method thereof.

According to an aspect of the invention, a waste heat utilization device includes a Rankine cycle in which an operation fluid circulates, and a control unit which controls an operation of the Rankine cycle. The Rankine cycle has a heater for heating the operation fluid using a waste fluid with a waste heat from a heat engine, an expander that expands the heated operation fluid to recover a mechanical energy, and a condenser for cooling and condensing the expanded operation fluid. The control unit operates the Rankine cycle when a waste fluid temperature is not less than a predetermined temperature and when the waste fluid is in a flowing state in the heat engine.

Because the control unit determines not only the waste fluid temperature but also the flowing state of the waste fluid, the Rankine cycle is ensured to be operated when the waste heat recovery is possible. As a result, the waste heat recovery can be performed effectively, and a fuel consumption rate of a vehicle can be improved.

According to another aspect of the invention, a control method of a waste heat utilization device including a Rankine cycle is provided. The Rankine cycle heats an operation fluid in the Rankine cycle by a heater using a waste fluid with a waste heat from a heat engine, expands the heated operation fluid by an expander for recovering a mechanical energy, and cools and condenses the expanded operation fluid by a condenser. The method includes a step of determining whether a waste fluid temperature is not less than a predetermined temperature, a step of determining whether the waste fluid is in a flowing state, and a step of operating the Rankine cycle when the waste fluid temperature is not less than the predetermined temperature and the waste fluid is in the flowing state.

By the above-described control method, the effects described in the former aspect of the invention can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

Additional objects and advantages of the present invention will be more readily apparent from the following detailed description of preferred embodiments when taken together with the accompanying drawings. In the drawings:

FIG. 1 is a schematic diagram showing a waste heat utilization device according to a first embodiment of the invention;

FIGS. 2A and 2B are cross-sectional views showing a compression/expansion unit according to the first embodiment;

FIG. 3 is a flow diagram showing a process performed by a control unit for controlling the waste heat utilization device according to the first embodiment;

FIG. 4 is a graph showing a relationship between a determination value and a temperature of a cooling water, set in the control unit, according to the first embodiment;

FIG. 5 is a schematic diagram showing an operation state of the waste heat utilization device according to the first embodiment when a refrigeration cycle is in operation;

FIG. 6 is a schematic diagram showing an operation state of the waste heat utilization device according to the first embodiment when a Rankine cycle is in operation;

FIG. 7 is a flow diagram showing a process performed by the control unit for a Rankine/air-conditioning cooperative control according to the first embodiment;

FIG. 8 is a graph showing a relationship between a determination value and a temperature of the cooling water at an evaporator temperature TE, set in the control unit, according to the first embodiment;

FIG. 9 is a time chart showing operation states in a normal air-conditioning control and the Rankine/air-conditioning cooperative control in the control unit according the first embodiment;

FIG. 10 is a schematic diagram showing a waste heat utilization device according to a second embodiment of the invention;

FIG. 11 is a flow diagram showing a process performed by a control unit for controlling the waste heat utilization device according to the second embodiment;

FIG. 12 is a graph showing a relationship between a determination value and a flow amount a cooling water, set in the control unit, according to the second embodiment;

FIG. 13 is a flow diagram showing a process performed by the control unit for a Rankine/air-conditioning cooperative control according to the second embodiment;

FIG. 14 is a schematic diagram showing a waste heat utilization device according to a third embodiment of the invention;

FIG. 15 is a schematic diagram showing a waste heat utilization device according to a fourth embodiment of the invention;

FIG. 16 is a flow diagram showing a process performed by a control unit for controlling the waste heat utilization device according to the fourth embodiment;

FIG. 17 is a flow diagram showing a process performed by the control unit for a Rankine/air-conditioning cooperative control according to the fourth embodiment;

FIG. 18 is a schematic diagram showing a waste heat utilization device according to a fifth embodiment of the invention;

FIG. 19 is a schematic diagram showing a waste heat utilization device according to a sixth embodiment of the invention;

FIG. 20 is a flow diagram showing a process performed by a control unit for controlling the waste heat utilization device according to the sixth embodiment;

FIG. 21 is a time chart showing a heat loss amount of a condenser, a required cooling capacity, and a rotation number of an expander according to the sixth embodiment;

FIG. 22 is a schematic diagram showing a waste heat utilization device according to a seventh embodiment of the invention; and

FIG. 23 is a schematic diagram showing a waste heat utilization device according to an eighth embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment

In a first embodiment, a waste heat utilization device 20 is typically used for a hybrid vehicle which has an electric motor 140 for driving, and an engine (heat engine) 10 being operated or stopped in accordance with a driving state of the vehicle. The waste heat utilization device 20 includes a refrigeration cycle 20A as a base cycle, and a Rankine cycle 30A for recovering an energy from a waste heat generated in the engine 10. At a compression part and expansion part of the cycles 20A and 30A, a compression/expansion unit 110 as a fluid machine is provided. The cycles 20A and 30 A, and the compression/expansion unit 110 are controlled by a control unit 40. The waste heat utilization device 20 according to the first embodiment will be described below with reference to FIG. 1.

The refrigeration cycle 20A moves heat from a low temperature side to a high temperature side for using a thermal energy for an air conditioning. The refrigeration cycle 20A includes the compression/expansion unit 110, a condenser 21, a gas-liquid separator 22, a decompressor 23, and an evaporator 24 which are connected to form a closed cycle.

The compression/expansion unit 110 is operated in both a compression mode (operating as a compressor) for compressing and discharging a gas refrigerant, and an expansion mode (operating as an expander) for converting a fluid pressure of a superheated vapor refrigerant during expansion to a kinetic energy and outputting a mechanical energy. The compression/expansion unit 110 is connected with a generator/motor 120 which functions as both a generator and a motor. When the compression/expansion unit 110 is operated in the compression mode, the generator/motor 120 functions as a power source for providing a motive power (R1) to the compression/expansion unit 110. When the compression/expansion unit 110 is operated in the expansion mode, the generator/motor 120 functions as the generator for generating an electric power by the motive power (R2) recovered at the compression/expansion unit 110. The electric power generated by the generator/motor 120 is charged in a battery, and is used for starting the engine 10 and an usual operating of various types of current consumer (e.g., headlight and engine auxiliary machine). Further detail about the compression/expansion unit 110 will be described below.

The condenser 21 is located on a refrigerant discharge side of the compression/expansion unit 110 in the refrigeration cycle 20A. The condenser 21 is a heat exchanger, which cools and condenses the high-temperature and high-pressure refrigerant discharged from the compression/expansion unit 110, by an outside air of a vehicle compartment flowing into a heat exchanging part of the condenser 21. The gas-liquid separator 22 is a receiver, which separates the refrigerant condensed in the condenser 21 into gas refrigerant and liquid refrigerant, and flows out the liquid refrigerant. The decompressor 23 decompresses and expands the liquid refrigerant separated by the gas-liquid separator 22. In this embodiment, the decompressor 23 has a thermal expansion valve for decompressing the liquid refrigerant in iso-enthalpy, and controlling a throttle open degree so that a super-heating degree of the refrigerant sucked into the compression/expansion unit 110 in the compression mode becomes a predetermined value.

The evaporator 24 is a heat exchanger which evaporates the refrigerant decompressed by the decompressor 23 for obtaining an endothermic effect, and cools air for air conditioning by the endothermic effect. A check valve 24 a is provided on a refrigerant outlet side of the evaporator 24 so that the refrigerant may flow only from the evaporator 24 to the compression/expansion unit 110.

The Rankine cycle 30A recovers the energy (i.e., a driving energy of the compression/expansion unit 110 in the expansion mode) from the waste heat generated in the engine 10 which generates a driving force of the vehicle. The Rankine cycle 30A uses the condenser 21 and the gas-liquid separator 22 in common with the refrigeration cycle 20A. Refrigerant bypasses the condenser 21 through a first bypass passage 31 connected from the gas-liquid separator 22 to a point A located between the compression/expansion unit 110 and the condenser 21, and a second bypass passage 32 connected from a point B located between the compression/expansion unit 110 and the check valve 24 a to a point C located between the condenser 21 and the point A.

In the first bypass passage 31, a liquid pump 33 and a check valve 31 a are provided so that the refrigerant may flow only from the gas-liquid separator 22 to the liquid pump 33. A heater 34 is provided between the point A and the compression/expansion unit 110. The heater 34 is a heat exchanger which heats the refrigerant by heat exchanging between the refrigerant (operation fluid) sent by the liquid pump 33 and an engine-cooling water (waste fluid) of a hot water circuit 10A of the engine 10.

A water pump 12 is a mechanical pump which circulates the engine-cooling water in the hot water circuit 10A, and is driven by the engine 10. A water radiator 13 is a heat exchanger which cools the engine-cooling water by heat exchanging between the engine-cooling water and the outside air.

On an outlet side of the hot water circuit 10A, a temperature sensor 14 for detecting a temperature of the engine-cooling water is provided. The temperature detected by the temperature sensor 14 is input to the control unit 40 as a signal. The engine 10 has a rotation speed sensor (rotation number detector) 15 for detecting a rotation number. The rotation number detected (output) by the rotation speed sensor 15 is input to the control unit 40 as a signal, similarly to the temperature.

In the second bypass passage 32, a check valve 32 a is provided so that the refrigerant may flow only from the compression/expansion unit 110 to a refrigerant inlet side of the condenser 21. Between the point A and the point C, a switching valve 35 is provided. The switching valve 35 is an electromagnetic valve for opening and closing a refrigerant passage, and is controlled by the control unit 40. On the refrigerant discharge side of the compression/expansion unit 110 in the compression mode, a control valve 36 is provided. When the compression/expansion unit 110 is operated in the compression mode, the control valve 36 functions as a check valve for stopping a discharge of the refrigerant. On the other hand, when the compression/expansion unit 110 is operated in the expansion mode, the control valve 36 becomes an open state. The control valve 36 is operated by the control unit 40.

The Rankine cycle 30A includes the gas-liquid separator 22, the first bypass passage 31, the liquid pump 33, the heater 34, the compression/expansion unit 110, the second bypass passage 32, and the condenser 21.

Next, a structure and an operation of the compression/expansion unit 110 will be described. In this embodiment, the compression/expansion unit 110 is constructed with a vane-type fluid machine. FIG. 2A shows the compression/expansion unit 110 in the compression mode, and FIG. 2B shows the compression/expansion unit 110 in the expansion mode.

When the compression/expansion unit 110 is operated in the compression mode, the control valve 36 functions as the check valve, and a rotor 120 a is rotated by the generator/motor 120 for sucking and compressing the refrigerant. The discharged high-pressure refrigerant is prevented from regurgitating to the side of the rotor 120 a by the control valve 36.

When the compression/expansion unit 110 is operated in the expansion mode, the control valve 36 is opened. The superheated vapor generated in the heater 34 is sucked into the compression/expansion unit 110 and is expanded for rotating the rotor 120 a and changing the thermal energy to the mechanical energy. Thus, a rotational force is generated by the compression/expansion unit 110 in the expansion mode.

As shown in FIG. 1, the control unit 40 is input with an air-conditioning (A/C) request signal, the signal from the temperature sensor 14, and the signal from the rotation speed sensor 15, for example. The air-conditioning request signal is determined in accordance with a setting temperature set by an occupant, an environmental condition (e.g., outside air temperature and amount of solar radiation entering into the vehicle compartment), for example. The control unit 40 controls components such as the liquid pump 33, the switching valve 35, the compression/expansion unit 110, the control valve 36 and the generator/motor 120 based on the input signals.

Next, a control operation of the waste heat utilization device 20 performed by the control unit 40 according to the first embodiment will be described with reference to a flow diagram in FIG. 3

At first, at step S110, it is determined whether or not there is the air-conditioning request from the occupant. When it is determined that there is the air-conditioning request (YES), it proceeds to step S120, and determines whether or not the temperature of the engine-cooling water is a sufficient temperature for heating the refrigerant at the heater 34, based on the signal from the temperature sensor 14.

As shown in FIG. 4, when the temperature of the engine-cooling water increases from a temperature lower than a second predetermined temperature Tw2 to the second predetermined temperature Tw2 and over, it is determined that the temperature of engine-cooling water becomes the sufficient temperature for heating (determination value 1). When the temperature of the engine-cooling water decreases to be lower than a first predetermined temperature Tw1 which is lower than the second predetermined temperature Tw2, it is determined that the temperature of the engine-cooling water is not the sufficient temperature for heating (determination value 0). In this way, a hysteresis is provided for determining the temperature of the engine-cooling water. The first predetermined temperature Tw1 and the second predetermined temperature Tw2 are determined so that a difference between the Tw1 and Tw2 is 5 to 10 deg, for example.

When it is determined that the temperature of engine-cooling water is not the sufficient temperature for heating (NO) at step S120, it proceeds to step S130. Then, a normal air-conditioning control is performed, and the refrigeration cycle 20A is continuously operated. Specifically, in the state that the liquid pump 33 is stopped, the switching valve 35 is opened, and the control valve 36 is functioned as the check valve, the generator/motor 120 is supplied with electricity for rotating the rotor 120 a. Thus, the refrigerant circulates in order of the compression/expansion unit (compressor) 110, the heater 34, the condenser (heat waster) 21, the gas-liquid separator 22, the decompressor 23, the evaporator (heat sink) 24, and the compression/expansion unit (compressor) 110, as shown in FIG. 5. The rotation number of the rotor 120 a (i.e., rotation number of the compressor) is controlled based on a first target temperature TEO1 (e.g., first target temperature of the engine-cooling water or that of other part associated with the engine-cooling water temperature) at the evaporator outlet which is calculated in accordance with values input from various sensors, such as the outside air temperature, the air conditioning setting temperature, and the amount of solar radiation entering into the vehicle compartment. After step S130 is performed, it retunes to step S110, and the following steps in FIG. 3 are repeated.

When it is determined that the temperature of the engine-cooling water is the sufficient temperature for heating (YES) at step S120, it proceeds to step S140. Then, a Rankine/air-conditioning cooperative control is performed, and the operation of the Rankine cycle 30A and the operation of the refrigeration cycle 20A are appropriately switched. The detail about the Rankine/air-conditioning cooperative control will be described below. After step S140 is performed, it retunes to step S110, and the following steps in FIG. 3 are repeated.

At step S110, when it is determined that there is not the air-conditioning request (NO), it proceeds to step S150 and determines whether or not the temperature of engine-cooling water is the sufficient temperature for heating the refrigerant at the heater 34, based on the signal from the temperature sensor 14, similarly to that of step S120. When it is determined that the temperature of the engine-cooling water is the sufficient temperature for heating (YES), it proceeds to step S160, and determines whether or not the engine 10 is in operation (operation state) based on the signal from the rotation speed sensor 15. When it is determined that the engine 10 is in operation (ON), it is determined that a flow amount of the engine-cooling water is sufficient amount for heating the refrigerant at the heater 34 (i.e., the engine-cooling water is in a flowing state) because the water pump 12 is operated by the engine 10. Then, it proceeds to step S170, and the Rankine cycle 30A is operated.

Specifically, in the state that the switching valve 35 is closed and the control valve 36 is opened, the liquid pump 33 is operated. Thus, the refrigerant circulates in order of the gas-liquid separator 22, the first bypass passage 31, the liquid pump 33, the heater 34, the compression/expansion unit (expander) 110, the second bypass passage 32, the condenser 21, and the gas-liquid separator 22, as shown in FIG. 6. When the Rankine cycle 30A is in operation, the rotation number of the generator/motor 120 is controlled in accordance with the temperature of the engine-cooling water so that the maximum generated output can be obtained at the generator/motor 120. After step S170 is performed, it retunes to step S110, and the following steps in FIG. 3 are repeated.

When it is determined that the temperature of engine-cooling water is not the sufficient temperature for heating (NO) at step S150, or when the engine 10 is not in operation (NO) (i.e., the engine-cooling water is not in the flowing state) at step S160, it proceeds to step S180. Then, the liquid pump 33 is stopped, the supply of electricity to the generator/motor 120 is stopped, and the Rankine cycle 30A and the refrigeration cycle 20A are not operated (OFF). After step S180 is performed, it retunes to step S110, and the following steps in FIG. 3 are repeated.

Next, the detail about the Rankine/air-conditioning cooperative control performed at step S140 will be described with reference to a flow diagram in FIG. 7.

At step S210, a second target temperature TEO2 (e.g., second target temperature of the engine-cooling water or that of other part associated with the engine-cooling water temperature) at the evaporator outlet used for the Rankine/air-conditioning cooperative control is calculated. Specifically, the first target temperature TEO1 at the evaporator outlet same as that used for the normal air conditioning control (step S130 in FIG. 3) is calculated in accordance with the values input from various sensors such as the outside air temperature, the air-conditioning setting temperature, and the amount of solar radiation entering into the vehicle compartment. Then, the second target temperature TEO2 at the evaporator outlet is determined to be lower than TEO1 by a predetermined value, e.g., 1 to 5 deg.

At step S220, it is determined whether or not the engine 10 is in operation based on the signal from the rotation speed sensor 15, similarly to step S160. When it is determined that the engine 10 is in operation (ON), it is determined that the flow amount of the engine-cooling water is sufficient for heating the refrigerant at the heater 34 (i.e., the engine-cooling water is in the flowing state), and a waste heat amount from the engine 10 is sufficient amount for the operation of the Rankine cycle 30A. Then, it proceeds to step S230, and determines whether or not the operation of the refrigeration cycle 20A is requested. When it is determined that the operation of the refrigeration cycle 20A is not requested (NO), it proceeds to step S240, and the control valve 36, the switching valve 35, and the liquid pump 33 are controlled so that the Rankine cycle 30A is operated. After step S240 is performed, it returns to a routine of the whole control in FIG. 3.

A necessity of an operation of the refrigeration cycle 20A is determined by a comparison of the second target temperature TEO2 at the evaporator outlet and an actual temperature TE (e.g., actual temperature of the engine-cooling water or that of other part associated with the engine-cooling water temperature) at the evaporator outlet. Specifically, as shown in FIG. 8, a third target temperature TEO3 (e.g., third target temperature of the engine-cooling water or that of other part associated with the engine-cooling water temperature) is set to be higher than the TEO2 by a predetermined value. When the actual temperature TE increases from a temperature lower than the third target temperature TEO3 to the third target temperature TEO3 and over, it is determined that the operation of the refrigeration cycle 20A is requested (determination value is 1). On the other hand, when the actual temperature TE decreases to be lower than the second target temperature TEO2, it is determined that the operation of the refrigeration cycle 20A is not requested (determination value 0). In this way, a hysteresis is provided for the determination whether or not the operation of the refrigeration cycle 20A is requested. In this embodiment, the target temperatures TEO1, TEO2, TEO3 are target air temperatures to be cooled by the evaporator 24.

At step S220, when it is determined that the engine 10 is not in operation (OFF), it proceeds to step S250, the rotation number of the compression/expansion unit (compressor) 110, i.e., the rotation number of the rotor 120 a is calculated based on the second target temperature TEO2. Then, at step S260, the generator/motor 120 is supplied with electricity for rotating the rotor 120 a at the rotation number calculated at step S250, and the liquid pump 33, the switching valve 35, and the control valve 36 are controlled so that the refrigeration cycle 20A is operated. After step S260 is performed, it returns to the routine of the whole control in FIG. 3.

In this way, in the Rankine/air-conditioning cooperative control, when the refrigeration cycle 20A is operated, the target temperature at the evaporator outlet is set to be the second target temperature TEO2 which is lower than the first target temperature TEO1 used in the normal air-conditioning control (i.e., satisfying a required cooling capacity). Thus, a discharge amount of the compression/expansion unit (compressor) 110 is increased so that a cooling capacity becomes over the required cooling capacity. Therefore, even when the air conditioning is requested, it may obtain a time for which the refrigeration cycle 20A is not operated, without reducing the cooling capacity than that in the normal air-conditioning control, and may use the time for operating the Rankine cycle 30A.

FIG. 9 shows the compressor rotation number of the compression/expansion unit 110 in each of the normal air-conditioning control (step S130 in FIG. 3) and the Rankine/air-conditioning cooperative control (step S140 in FIG. 3), and operation state of the Rankine cycle 30A in the Rankine/air-conditioning cooperative control in accordance with a change in the rotation number of the engine 10. In the normal air-conditioning control, the compression/expansion unit (compressor) 110 is continuously operated in accordance with a cooling load. However, in the Rankine/air-conditioning cooperative control, when the refrigeration cycle 20A is operated, the rotation number of the compression/expansion unit (expander) 110 is set to be higher, and when the refrigeration cycle 20A is stopped, the Rankine cycle 30A is operated. The Rankine cycle 30A is generally stopped when the refrigeration cycle 20A is operated.

As described above, according to this embodiment, in the hybrid vehicle in which the engine 10 may be stopped even when the vehicle is in use, when it is determined whether or not the Rankine cycle 30A should be operated, the control unit 40 does not only determine whether or not the engine-cooling water of the engine 10 is the sufficient temperature for heating the refrigerant, but also determines whether or not the engine 10 is in operation, for confirming the flow amount of the engine-cooling water. When the engine 10 is not in operation, the control unit 40 determines that the engine-cooling water is not in the flowing state, and the Rankine cycle 30A is not operated. Therefore, the Rankine cycle 30A can be certainly operated only when the waste heat from the engine 10 is recoverable. As a result, the waste heat recovery can be performed effectively, and a fuel consumption rate of the vehicle can be improved.

In addition, even when the air conditioning is requested, if the temperature of the engine-cooling water is sufficient temperature for heating the refrigerant, the control unit 40 may set the time for which the refrigeration cycle 20A can be stopped while the engine 10 is in operation, and the time is used for operating the Rankine cycle 30A. As a result, the waste heat recovery can be performed effectively by using the waste heat utilization device 20.

Second Embodiment

A second embodiment of the invention will be described with reference to FIG. 10. In the first embodiment, the control unit 40 determines whether or not the flow amount of the engine-cooling water is sufficient amount, based on the signal of the rotation number of the engine 10. However, in the second embodiment, a flow amount sensor (flow amount detector) 41 is provided in the hot water circuit 10A for detecting the flow amount directly. A signal from the flow amount sensor 41 is input to the control unit 40. In the second embodiment, the water pump 12 may be the mechanical pump driven by the engine 10 similarly to the first embodiment, or may be an electric pump driven by an electric motor.

FIG. 11 is a flow diagram showing a control operation of the waste heat utilization device 20 by the control unit 40 according to the second embodiment. Steps S110 to 130, S150, S170, and S180 are same as those of the first embodiment.

In the first embodiment, it is determined whether or not the engine 10 is in operation, based on the signal of the rotation number, at step S160 in FIG. 3. However, the second embodiment, step S165 is used instead of step S160 in FIG. 3, and step 165 determines whether or not the flow amount of the engine-cooling water is sufficient amount based on the signal from the flow amount sensor 41, as shown in FIG. 11.

Specifically, as shown in FIG. 12, when the flow amount of the engine-cooling water detected by the flow amount sensor 41 increases from a flow amount smaller than a second predetermined flow amount Qw2 to the second predetermined flow amount Qw2 and over, it is determined that the flow amount is sufficient for heating the refrigerant (determination value 1). On the other hand, when the flow amount decreases to be smaller than a first predetermined flow amount Qw1 which is less than the second predetermined flow amount Qw2, it is determined that the flow amount is not sufficient for heating (determination value 0). In this way, a hysteresis is provided for the determination of the flow amount. The difference of the predetermined flow amount Qw1 and the second predetermined flow amount Qw2 may be set to be 2 L/min, for example.

FIG. 13 shows a control process in the Rankine/air-conditioning cooperative control performed at step S145 in FIG. 11. Steps S210, and S230 to S260 are same as those of the first embodiment. At step S225, the determination of the flow amount is performed similarly to step S165 in FIG. 11.

As described above, according to the second embodiment, the flow amount sensor 41 directly detects the flow amount of the engine-cooling water for the determination of the flow amount. Therefore, it can be determined more properly whether or not the flow amount is sufficient for heating, and the Rankine cycle 30A can be operated for longer time.

Third Embodiment

A third embodiment of the invention is described with reference to FIG. 14. In the first and second embodiments, the integral compression/expansion unit 110 formed by one fluid machine is used as the expander and the compressor. However, as shown in FIG. 14, it may use a compressor 130 and an expander 131 which are independent from each other, as the compression/expansion unit. The compressor 130 and the expander 131 are located in parallel with respect to a refrigerant flow, and switching valves 38 a and 38 b are provided in refrigerant passages connected to the compressor 130 and the expander 131. The waste heat utilizing device 20 may be controlled by the control unit 40 similarly to the first embodiment or the second embodiment. However, when the Rankine cycle 30A and the refrigeration cycle 20A are switched, the switching valves 38 a and 38 b are controlled by the control unit 40, as well as the liquid pump 33 and the switching valve 35.

Fourth Embodiment

A fourth embodiment of the invention will be described with reference to FIG. 15 to FIG. 17. In the fourth embodiment, as a pump for circulating the engine-cooling water in the hot water circuit 10A, an electric water pump 12 a is provided.

The water pump 12 a is driven by a generator, and is controlled by the controller (not shown) of the engine 10. Therefore, the water pump 12 a may be operated independently from the operation state of the engine 10 unlike the mechanical water pump 12. In the hybrid vehicle, the engine 10 may be stopped in accordance with the driving state of the vehicle. According to the first embodiment, the mechanical water pump 12 is stopped when the engine 10 is stopped. However, the electric water pump 12 a may be operated for circulating the engine-cooling water in the hot water circuit 10A, even when the engine 10 is stopped.

An operation signal which shows the operation state of the water pump 12 a is input to the control unit 40 from the controller of the engine 10. When the water pump 12 a is in operation, the control unit 40 determines that the engine-cooling water in the hot water circuit 10A is in the flowing state. When the water pump 12 a is not in operation, the control unit 40 determines that the engine-cooling water is not in the flowing state.

The operation (i.e., control process by the control unit 40) of the waste heat utilization device 20 according to the fourth embodiment will be described with reference to flow diagrams in FIG. 16 and FIG. 17. In the flow diagrams in FIG. 16 and FIG. 17, steps S166 and S266 are used instead of steps S160 and S220 in FIG. 3 and FIG. 7, respectively.

When it is determined that the air conditioning is not requested (NO) at step S110, and it is determined that the temperature of the engine-cooling water is sufficient for heating (YES) at step S150, it proceeds to step S166, and determines the operation state of the water pump 12 a. When the water pump 12 a is in operation (ON), the engine-cooling water is in the flowing state. Therefore, the refrigerant can be heated at the heater 34, and the Rankine cycle 30A is operated at step S170.

When the water pump 12 a is not operated (OFF), the engine-cooling water is not in the flowing state. Therefore, the refrigerant cannot be heated at the heater 34, and the Rankine cycle 30A is not operated at step S180.

When it is determined that the air conditioning is requested (YES) at step S110, and it is determined that the temperature of the engine-cooling water is sufficient for heating (YES) at step S120, it proceeds to S140, and the Rankine/air-conditioning cooperative control is performed. In the Rankine/air-conditioning cooperative control of FIG. 17, after calculating the second target temperature TEO2 at the evaporator outlet at step S210, it proceeds to step S266, and determines the flowing state of the engine-cooling water based on the operation state of the water pump 12 a, similarly to step S166. Then, the operation of the Rankine cycle 30A of step S240 and the operation of the refrigeration cycle 20A of step S260 are switched in accordance with the determination at step S266.

As described above, in the fourth embodiment, the electric water pump is used as the water pump 12 a. Therefore, the flowing state of the engine-cooling water can be determined exactly in accordance with the operation state of the water pump 12 a. Therefore, the effects described in the first embodiment can be obtained.

The control unit may determine that the engine-cooling water is in the flowing state when the rotation number of the water pump 12 a is a predetermined rotation number and over, and may determine that the engine-cooling water is not in the flowing state when the rotation number is under the predetermination number.

Fifth Embodiment

A fifth embodiment of the invention will be described with reference to FIG. 18. The Rankine cycle 30A of the waste heat utilization device 20 according to the fifth embodiment is similar to that of the fourth embodiment, but the refrigeration cycle 20A described in the fourth embodiment (FIG. 15) is not provided. Therefore, the air-conditioning request signal is not input to the control unit 40.

The waste heat utilization device 20 includes mainly the Rankine cycle 30A. The expander 131 is used instead of the compression/expansion unit 110, and the check valves 31 a and 32 a, the switching valve 35, and the control valve 36 are not provided. The expander 131, the condenser 21, the gas-liquid separator 22, the liquid pump 33, and the heater 34 are connected in order in a closed circuit, for forming the Rankine cycle 30A.

The control unit 40 controls the operation of the Rankine cycle 30A by using steps S150, S166, S170, S180 in the flow diagram in FIG. 16. The Rankine cycle 30A is operated in accordance with the temperature of the engine-cooling water and the flowing state of the engine-cooling water. Therefore, the waste heat can be recovered effectively.

Sixth Embodiment

A sixth embodiment of the invention will be described with reference to FIG. 19 to FIG. 21. In the sixth embodiment, a refrigeration cycle 20B is added to the waste heat utilization device 20 according to the fifth embodiment. The refrigeration cycle 20B has the compressor 130 for its own use, and using the condenser 21 and the gas-liquid separator 22 in common with the Rankine cycle 30A.

The refrigeration cycle 20B is formed as below by using a branch passage 25 provided in the Rankine cycle 30A. That is, the branch passage 25 is formed so as to be branched from a liquid-gas outlet side of the gas-liquid separator 22 and connected to a point D which is located between the expander 131 and the condenser 21. In the branch passage 25, the decompressor 23, the evaporator 24, and the compressor 130 are provided in this order. Thus, the compressor 130, the condenser 21, the gas-liquid separator 22, the decompressor 23, and the evaporator are connected in order in a closed circuit, for forming the refrigeration cycle 20B.

Because the refrigeration cycle 20B includes the compressor 130 for its own use, the refrigeration cycle 20B can be operated independently from the Rankine cycle 30A. That is, in the waste heat utilization device 20 according to the sixth embodiment, a single operation of the Rankine cycle 30A, a single operation of the refrigeration cycle 20B, and a simultaneous operation of the Rankine cycle 30A and the refrigeration cycle 20B can be performed.

The control operation of the waste heat utilization device 20 by the control unit 40 according to the sixth embodiment will be described with reference to FIG. 20. In a flow diagram in FIG. 20, step S121 is added to the flow diagram in FIG. 16 described in the fourth embodiment, and steps S131, S141, S171, and S181 are used instead of steps S130, S140, S170, and S180 in FIG. 16, respectively.

At first, it is determined whether or not there is the air-conditioning request from the occupant at step S110. When it is determined that the there is not the air-conditioning request (NO), it proceeds to step S150, and determines whether or not the temperature of the engine-cooling water is sufficient for heating the refrigerant at the heater 34, based on the signal form the temperature sensor 14.

When it is determined that the temperature of the engine-cooling temperature is sufficient for heating (YES), it proceeds to step S166, and determines the flowing state of the engine-cooling water based on the operation state of the water pump 12 a. When it is determined that the engine-cooling water is in the flowing state (YES) at step S166, it proceeds to step S171, and the single operation (single control) of the Rankine cycle 30A is performed (i.e., the refrigeration cycle 20B is not operated).

When it is determined that the temperature of the engine-cooling water is not sufficient for heating (NO) at step S150, or when it is determined that the water pump 12 a is not in the operation state (OFF) and the engine-cooling water is not in the flowing state at step S166, it proceeds to step S181, and neither the Rankine cycle 30A nor the refrigeration cycle 20B is operated.

When it is determined that there is the air-conditioning request from the occupant (YES) at step S100, it proceeds to step S120, and determines whether or not the temperature of the engine-cooling water is sufficient for heating the refrigerant at the heater 34.

When the temperature of the engine-cooling water is not sufficient for heating (NO) at step S120, it proceeds to step S131, an air-conditioning single operation (normal air-conditioning control) is performed, and only the refrigeration cycle 20B is operated (i.e., the Rankine cycle 30A is not operated).

However, when it is determined that the temperature of the engine-cooling water is sufficient for heating (YES) at step S120, it proceeds to step S121, and determines the flowing state of the engine-cooling water based on the operation state of the water pump 12 a. When it is determined that the engine-cooling water is not in the flowing state (NO), it proceeds to step S131, and the air-conditioning single operation is performed. On the other hand, when it is determined that engine-cooling water is in the flowing state (YES), it proceeds to step S141, a Rankine/air-conditioning simultaneous operation (simultaneous operation control) is performed, and both the Rankine cycle 30A and the refrigeration cycle 20B are simultaneously operated.

FIG. 21 shows the relationship between a required cooling capacity, a rotation number of the expander 131, and a heat loss amount of the condenser 21, in the Rankine/air-conditioning simultaneous operation.

In the Rankine/air-conditioning simultaneous operation, the control unit 40 controls the rotation number of the expander 131 of the Rankine cycle 30A so that a heat loss amount at the condenser 21 does not exceed its heat loss capacity. That is, the control unit 40 determines the heat loss capacity at the condenser 21 as shown by dotted line A in FIG. 21 based on the outside air temperature flowing into the heat exchanging part of the condenser 21, the flow rate of the outside air, and the size of the condenser 21.

When the refrigeration 20B is operated, the heat loss corresponding to a heat quantity absorbed by the refrigerant at the evaporator 24, and a heat quantity received from compression at the compressor 130, is required at the condenser 21 for providing the cooling capacity required for air conditioning. The control unit 40 determines the heat loss amount of the condenser 21 as a refrigeration cycle heat loss amount (first heat loss amount) shown by the lower area under the line B in FIG. 21.

When the Rankine cycle 30A is operated, a heat loss for cooling and condensing the refrigerant flowing from the expander 131 is required at the condenser 21. The control unit 40 determines the heat loss amount as the Rankine cycle heat loss amount (second heat loss amount) shown by the upper area above the line B in FIG. 21. The Rankine cycle heat loss amount is proportional to the flow amount of the refrigerant flowing into the condenser 21, i.e., the rotation number of the expander 131 as shown in FIG. 21.

Therefore, when the Rankine/air-conditioning simultaneous operation is performed, the control unit 40 controls the rotation number of the expander 131 so that the sum of the heat loss amount of the refrigeration cycle 20B and the heat loss amount of the Rankine cycle 30A is not more than the heat loss capacity of the condenser 21. That is, when the required cooling capacity of the refrigeration cycle 20B is low, the rotation number of the expander 131 is increased, and the recovering energy (generated energy) of the Rankine cycle 30A is increased. On the other hand, when the required cooling capacity of the refrigeration cycle 20B is high, the rotation number of the expander 131 is decreased, and the driving force for recovery (generated energy) of the Rankine cycle 30A is decreased.

As described above, according to the sixth embodiment of the invention, the refrigeration cycle 20B having the compressor 130 for its own use and using the condenser 21 and the gas-liquid separator 22 in common with the Rankine cycle 30A is provided. Therefore, the Rankine single operation, the air-conditioning single operation, and the Rankine/air-conditioning simultaneous operation can be selectively performed. The Rankine cycle 30A is operated in accordance with the temperature of the engine-cooling water and the flowing state of the engine-cooling water. Therefore, the waste heat can be recovered effectively.

When the Rankine/air-conditioning simultaneous operation is performed, the control unit 40 controls the rotation number of the expander 131 so that the sum of the heat loss amount of the refrigeration cycle 20B and the heat loss amount of the Rankine cycle 30A is not more than the heat loss capacity of the condenser 21. Therefore, the required cooling capacity can be obtained by the refrigeration cycle 20B and the waste heat can be effectively recovered by the Rankine cycle 30A without breaking down of the heat loss function of the condenser 21.

Seventh Embodiment

A seventh embodiment of the invention will be described with reference to FIG. 22. A waste heat utilization device 20 according to the seventh embodiment is similar to that of the sixth embodiment, but the mechanical water pump 12 is used instead of the electric water pump 12 a, and the rotation speed sensor 15 is added to the engine 10. The water pump 12 and the rotation speed sensor 15 are similar to those in the first embodiment.

According to the seventh embodiment, the determination of the operation state of the engine 10 based on the signal from the rotation sensor 15 is performed instead of the determination of the flowing state of the engine-cooling water at steps S121 and S166 in FIG. 20 described in the sixth embodiment. Therefore, the effects described in the sixth embodiment can be obtained.

Eighth Embodiment

An eighth embodiment of the invention will be described with FIG. 23. In a waste heat utilization device 20 according to the eighth embodiment, the refrigeration cycle 20B in the seventh embodiment is not provided, however the other parts of the waste heat utilization device 20 are similar to those of the above-described seventh embodiment. The waste heat utilization device 20 according to the eighth embodiment can be made similar to that of the fifth embodiment (FIG. 18), but the mechanical water pump 12 is used instead of the electric water pump 12 a in the fifth embodiment.

The Rankine cycle 30A is operated by the control unit 40 in accordance with the temperature of the engine-cooling water obtained by the temperature sensor 14, and the operation state of the engine 10 (the flowing state of the engine-cooling water) obtained by the rotation speed sensor 15. Therefore, the waste heat can be recovered effectively.

Other Embodiments

Although the present invention has been fully described in connection with the preferred embodiments thereof with reference to the accompanying drawings, it is to be noted that various changes and modifications will become apparent to those skilled in the art.

For example, according to the above-described first, third, seventh, and eighth embodiments, the operation state of the engine 10 is determined based on the rotation number of the engine 10 detected by the rotation speed sensor 15. However, as a substitute for the rotation number of the engine 10, it may use a suction pressure of the engine 10 and an opening degree of a suction throttle valve, for example.

According to the above-described second embodiment, the flow amount sensor 41 is located between the engine 10 and the heater 34. However, the flow amount sensor 41 may be located adjacent to the engine-cooling water outlet side of the heater 34, and herewith an accurate flowing state of the waste fluid at the heater 34 can be detected without an affect of the delay of a response time of the flow amount sensor 41.

In the above-described embodiments, the cooling water of the engine 10 is used as the waste fluid of the heat engine. However, an exhaust gas may be directly used as the waste fluid.

In addition, in the above-described embodiments, the Rankine cycle 30A and the waste heat utilization device 20 are used for the hybrid vehicle. However, they may be used for an idling stop vehicle in which the engine 10 is operated and stopped in accordance with a vehicle driving state. Furthermore, they may be used for a normal vehicle including the engine 10.

Such changes and modifications are to be understood as being within the scope of the present invention as defined by the appended claims. 

1. A waste heat utilization device comprising: a Rankine cycle in which an operation fluid circulates, the Rankine cycle including: a heater for heating the operation fluid using a waste fluid with a waste heat from a heat engine; an expander that expands the heated operation fluid to recover a mechanical energy; and a condenser for cooling and condensing the expanded operation fluid; and a control unit which controls an operation of the Rankine cycle, wherein: the control unit operates the Rankine cycle when a waste fluid temperature is not less than a predetermined temperature and when the waste fluid is in a flowing state in the heat engine.
 2. The waste heat utilization device according to claim 1, wherein: the control unit sets the predetermined temperature to have a hysteresis by using a first predetermined temperature, and a second predetermined temperature which is higher than the first predetermined temperature.
 3. The waste heat utilization device according to claim 1, wherein: the control unit determines the flowing state of the waste fluid based on an operation state of the heat engine.
 4. The waste heat utilization device according to claim 3, further comprising: a rotation number detector for detecting a rotation number of the heat engine, wherein: the control unit determines the operation state of the heat engine based on the detected rotation number.
 5. The waste heat utilization device according to claim 1, wherein: the waste fluid is a cooling water for cooling the heat engine; and the Rankine cycle further includes a mechanical pump which is driven by the heat engine to send the cooling water to the heater.
 6. The waste heat utilization device according to claim 1, further comprising: a flow amount detector for detecting a flow amount of the waste fluid, wherein: the control unit determines that the waste fluid is in the flowing state when the flow amount is not less than a predetermined flow amount.
 7. The waste heat utilization device according to claim 6, wherein: the control unit sets the predetermined flow amount to have a hysteresis by using a first predetermined flow amount, and a second flow amount which is greater than the first predetermined flow amount.
 8. The waste heat utilization device according to claim 7, wherein: the second predetermined flow amount is set to be greater than the first predetermined flow amount approximately by 2 L/min.
 9. The waster heat utilization device according to claim 6, wherein: the flow amount detector is provided adjacent to a waste fluid outlet side of the heater.
 10. The waste heat utilization device according to claim 1, further comprising: an electric pump for circulating the waste fluid to the heater, wherein: the control unit determines the flowing state of the waste fluid based on an operation state of the electric pump.
 11. The waste heat utilization device according to claim 1, further comprising: a refrigeration cycle having a compressor for compressing and discharging a refrigerant in the refrigeration cycle, the compressor being provided to be also used as the expander or being arranged to be parallel to the expander, wherein: the condenser is used in common in the refrigeration cycle and the Rankine cycle; the control unit controls operation of the compressor when an operation of the refrigeration cycle is required and the waste fluid temperature is not less than the predetermined temperature; and the control unit operates the Rankine cycle when the compressor is not operated.
 12. The waste heat utilization device according to claim 11, wherein: the control unit increases a discharge amount of the compressor so that a cooling capacity of the refrigeration cycle is not less than a required cooling capacity when the control unit operates the compressor.
 13. The waste heat utilization device according to claim 12, wherein: the control unit increases the discharge amount of the compressor so that the waste fluid temperature at an evaporator of the refrigeration cycle or a temperature of other part associated with the waste fluid temperature becomes a second target temperature which is lower than a first target temperature satisfying the required cooling capacity.
 14. The waste heat utilization device according to claim 13, wherein: the control unit sets the second target temperature to be lower than the first target temperature approximately by 1 to 5 degree.
 15. The waste heat utilization device according to claim 1, further comprising: a refrigeration cycle having a compressor for compressing and discharging a refrigerant in the refrigeration cycle, the refrigeration cycle using the condenser in common with the Rankine cycle and controlled by the control unit independently from the Rankine cycle, wherein: the control unit simultaneously operates the refrigeration cycle and the Rankine cycle, when the operation of the refrigeration cycle is required, the waste fluid temperature is not less than the predetermined temperature, and the waste fluid is in the flowing state.
 16. The waste heat utilization device according to claim 15, wherein: the control unit controls a rotation number of the expander so that the sum of a first heat loss amount required for condensing the operation fluid discharged from the compressor and a second heat loss amount required for condensing the operation fluid flowing out from the expander is not more than a heat loss capacity of condensing at the condenser.
 17. The waste heat utilization device according to claim 1, wherein: the heat engine is an internal combustion engine for a vehicle.
 18. The waste heat utilization device according to claim 17, wherein: the vehicle is a hybrid vehicle or an idling stop vehicle in which the internal combustion engine is operated and stopped in accordance with a driving state of the vehicle.
 19. A control method of a waste heat utilization device that comprises a Rankine cycle which heats an operation fluid in the Rankine cycle by a heater using a waste fluid with a waste heat from a heat engine, expands the heated operation fluid by an expander for recovering a mechanical energy, and cools and condenses the expanded operation fluid by a condenser, the method comprising: determining whether a waste fluid temperature is not less than a predetermined temperature; determining whether the waste fluid is in a flowing state; and operating the Rankine cycle when the waste fluid temperature is not less than the predetermined temperature and the waste fluid is in the flowing state.
 20. The control method of a waste heat utilization device according to claim 19, further comprising: setting the predetermined temperature to have a hysteresis by using a first predetermined temperature, and a second predetermined temperature which is higher than the first predetermined temperature.
 21. The control method of a waste heat utilization device according to claim 19, wherein: the determining of the flowing state of the waste fluid is performed based on an operation state of the heat engine.
 22. The control method of a waste heat utilization device according to claim 21, wherein: the operation state of the heat engine is determined based on a rotation number of the heat engine.
 23. The control method of a waste heat utilization device according to claim 19, wherein: the waste fluid is a cooling water for cooling the heat engine, and the waste fluid is sent to the heater by a mechanical pump driven by the heat engine.
 24. The control method of a waste heat utilization device according to claim 19, wherein: the waste fluid is determined in the flowing state when a flow amount of the waste fluid is not less than a predetermined flow mount.
 25. The control method of a waste heat utilization device according to claim 24, further comprising: setting a predetermined flow amount to have a hysteresis by using a first predetermined flow amount, and a second flow amount which is greater than the first predetermined flow amount.
 26. The control method of a waste heat utilization device according to claim 25, wherein: the second predetermined flow amount is set to be greater than the first predetermined flow amount approximately by 2 L/min.
 27. The control method of a waste heat utilization device according to claim 24, further comprising: detecting the flow amount of the waste fluid adjacent to a waste fluid outlet side of the heater.
 28. The control method of a waste heat utilization device according to claim 19, wherein: the flowing state of the waste fluid is determined based on an operation state of an electric pump for sending the waste fluid to the heater.
 29. The control method of a waste heat utilization device according to claim 19, wherein: the waste heat utilization device further comprises a refrigeration cycle having a compressor for compressing and discharging a refrigerant, the compressor being also used as the expander or being arranged to be parallel to the expander, wherein the refrigeration cycle uses the condenser in common with the Rankine cycle, the method further comprising: controlling operation of the compressor when an operation of the refrigeration cycle is required and the waste fluid temperature is not less than the predetermined temperature; and operating the Rankine cycle when the compressor is not operated.
 30. The control method of a waste heat utilization device according to claim 29, further comprising: increasing a discharge amount of the compressor so that a cooling capacity of the refrigeration cycle is not less than a required cooling capacity when the compressor is operated.
 31. The control method of the waste heat utilization device according to claim 30, wherein: the discharge amount of the compressor is increased so that the waste fluid temperature at an evaporator of the refrigeration cycle or a temperature of other part associated with the waste fluid temperature becomes a second target temperature which is lower than a first target temperature satisfying the required cooling capacity.
 32. The control method of a waste heat utilization device according to claim 31, further comprising: setting the second target temperature to be lower than the first target temperature approximately by 1 to 5 degree.
 33. The control method of a waste heat utilization device according to claim 19, wherein: the waste heat utilization device comprises a refrigeration cycle having a compressor for compressing and discharging a refrigerant in the refrigeration cycle, using the condenser in common with the Rankine cycle, and controlled by the control unit independently from the Rankine cycle, the method further comprising: simultaneously operating the refrigeration cycle and the Rankine cycle, when the operation of the refrigeration cycle is required, the waste fluid temperature is not less than the predetermined temperature, and the waste fluid is in the flowing state.
 34. The control method of the waste heat utilization device according to claim 33, further comprising: controlling a rotation number of the expander so that the sum of a first heat loss amount required for condensing the operation fluid discharged from the compressor and a second heat loss amount required for condensing the operation fluid flowing out from the expander is not more than a heat loss capacity of condensing at the condenser.
 35. The control method of the waste heat utilization device according to claim 19, wherein: the heat engine is an internal combustion engine for a vehicle.
 36. The control method of the waste heat utilization device according to claim 35, wherein: the vehicle is a hybrid vehicle or an idling stop vehicle in which the internal combustion engine is operated and stopped in accordance with a driving state of the vehicle. 